Condition responsive electric switch mechanism



Nov. 3, 1953 R. 1.. GRAY ET AL 2,658,121

CONDITION RESPONSIVE ELECTRIC SWITCH MECHANISM Filed July 30, 1951 2Sheets-Sheet l T -El.

. \nven'tons:

Robert L. GraH, Charles 5. Grimshaw,

Their" A-t'torneg Nov. 3, 1953 R. L. GRAY ET AL 2,658,121

CONDITION RESPONSIVEZ ELECTRIC SWITCH MECHANISM Filed July 30, 1951 2Sheets-Sheet 2 Inventors:

Robert 1... Gra g, Charles 5. Grimshaw,

T heir" Attovneg Patented Nov. 3, 1953 CONDITION RESPONSIVE ELECTRICSWITCH MECHANISM Robert L. Gray, Schenectady, N. Y., and Charles S.Grimshaw, Erie, Pa., assignors to General Electric Company, acorporation of New York Application July 30, 1951, Serial No. 239,338

13 Claims. 1

This invention relates to electric switch mechanisms, and moreparticularly to such mechanisms which are utilized in the automaticregulation of a condition such as temperature or pressure.

The principal object of our invention is to provide a conditionresponsive switch mechanism which is inexpensive and easy tomanufacture, and at the same time is reliable in operation and willprovide a long life.

A feature of the invention is the provision of a snap action switchmechanism employing a non-overcenter spring.

Other objects and advantages of our invention will be in part obviousand are in part pointed out in the subsequent detailed description of apreferred embodiment of the invention.

In carrying out our invention in one form. we provide a switch mechanismwhich includes a fixed contact, a movable contact mounted on acantilever spring, and a main operating lever arranged to move thecantilever spring member to open and close the contacts. The mainoperating lever is continually biased in the contacts closed directionby a non-overcenter spring. The operating lever is further biased in theopposite or contacts open direction by an additional spring whichnormally overpowers the non-overcenter spring and maintains and contactsopen. Condition responsive means are provided for partiallycounteracting the second spring under certain circumstances to such anextent that the non-overcenter spring is able to close the contacts.When the counteracting action lessens sufficiently, the contacts areagain opened.

For a clearer and more complete understanding of our invention,reference should be had to the accompanying drawing in which:

Fig. 1 is a side elevation View, partially in section, of a conditioncontrol device embodying our invention in a preferred form,

Fig. 2 is a left end View of the device of Fig. 1 ShOWing only afragmentary part of the control knob,

Fig. 3 is a side view, partially in section, similar to Fig. 1 exceptomitting some parts and showing the contacts in the closed position,

Fig. 4: is an end view similar to Fig. 2 except partially in section,

5 is a sectional view along the lines 5-5 of Fig. 1,

Fig. 6 is a sectional view along the lines 6--6 of Fig. 1,

Fig. '7 is an end view along the lines 1-! of Fig. 1,

Fig. 8 is a top view partially in section of the device of Fig. 1, and

Fig. 9 is a partial side view in section of the device of Fig. 1 showingthe details of the differential adjustment mechanism thereof.

In the drawing our invention is shown embodied in a refrigeratortemperature control device which is designated generally by the numerali8. As shown particularly in Figs. 1 and 3, this device includes asubstantially U-shaped metal frame or support member I I having twosubstantially horizontal legs, the lower of which has an ofiset portion,and a vertical connecting or bight portion, which is to the left inthese figures. The frame H has a vertical metal cross member I? rigidlyconnected between the two horizontal legs of member H, preferably bymeans of projections along the upper and lower edges of member I2 whichengage corresponding openings in member ll, while an additionalinsulating support member 13 closes the free ends of member ll.

Referring to Figs. 2 and 4 in addition to Figs. 1 and 3, the device it)includes a face plate l4 rigidly secured to the vertical bight portionof support member l in a suitable manner such as by a pair of rivets I5.As illustrated, the face plate It has a pair of countersunk tappedopenings It to provide for the attachment of device 10 to anotherapparatus or support. As seen best in Fig. 4, the device i0 alsoincludes a pair of side plates I! of insulating material enclosing ,therectangular opening formed by support member H and insulating supportmember [3. For ease of assembly, these insulating side members arepreferably arranged to be held in place along their lower edges byupturned side portions IQ of a bottom plate 18, and along their sideedges by right angle portions 15 of front plate Hi along one edge (seeFig. 8) and indentations 20 in insulating member [3 (one of which isshown in Fig. 3) along the other edge. As

"shown in Figs. 4 and 5, a U-shaped resilient member 2| fits down overthe top horizontal leg of frame member ll; member 2| preferably has aplurality of indentations 2m (as shown in Fig. 6) forming projections211) which snap into corresponding openings in side member ll, thusportions |.'-l form an auxiliary enclosure 11 beneath the lowerhorizontal member of frame H which houses a bellows 22. The bellows 22may be connected by an external tube 87 to a source of fluid underpressure which actuates the bellows under conditions hereinafterdiscussed. The bellows 22 is rigidly secured to bottom plate l8 and whenfluid pressure is applied to the inside of the bellows the upper surface23 thereof expands upwardly. The vertical spacing in the bellowsenclosure 'l! is preferably such that only a limited expansion of thebellows can take place before the upper surface of the bellows contactsthe frame member I, in order to prevent damage to the bellows in theevent of an abnormally high pressure. As an aid in firmly securing tube81, it may be held by a split bracket 4|] forming a downward right angleextension of plate |8.

The upper surface 23 of the bellows has a rectangular indentation 24located approximately centrally thereof in which is positioned arectangular vertical operating rod 25. The operating rod has shoulderportions 25a (see Fig. a short distance above the lower horizontal legof frame H, and a circular spring retaining member rests on theseshoulders. A suitable rectangular indentation is provided in the lowersurface of member 25 which engages the shoulders 25a and holds member 25in place. Circular member 25 also has an elongated slot at right anglesto the longitudinal axis of operating rod 25 and to the plane of Fig. 5,this slot being of such dimensions that the lower enlarged portion ofoperating rod 25 can be readily slipped through the slot in member 25during assembly. Then when operating rod 25 is subsequently turned 90 tothe position shown in Figs. 1, 3 and 5 and the indentation in the bottomsurface of retainer 26 is engaged with the shoulder portions 25a, of theoperating rod, the retaining ring is prevented from being dislodged.

The device l0 further includes a bracket 21 which is vertically slidablealong cross member l2 of the frame. Bracket Zl includes a pair ofvertically disposed right angle side members 28 which provide contactwith cross member l2 near the top and near the bottom thereof along eachside in order to provide a stable sliding bracket. Bracket 2'! alsoincludes a centrally positioned horizontal right-angle portion 29 havingan opening 30 therein through which rod 25 operates. A compressionspring 3| which opposes the expansion of bellows 22 is positionedbetween horizontal portion 29 of the slidable bracket 21 and retainingring 26.

Near the lower portion thereof, the bracket 21 is provided with a secondhorizontal projection 32 which extends (to the left in Figs. 1 and 3)through a suitable opening 33 in cross member l2. Extension 33 providesmeans for the vertical movement of bracket 21, and may have a set screw34 positioned in a suitable tapped opening therein. The set screw 34rides on a cam 35 (best seen in 2 and 4) which provides for a move mentof bracket 2'! upwardly and downwardly, with consequent changes in theforce exerted by spring 3!. In Fig. 2, the cam is shown in the positionwhich allows the greatest rise of bracket 21 thereby producing theminimum compression in spring 4|. In Fig. 4, the cam is shown rotatedthrough almost a complete revolution counterclockwise from Fig. 2 to theposition which produces the maximum downward movement of bracket 21 andconsequently the greatest compressive force on spring 3|.

. cal cross member I2 of the frame.

The cam 35 may be integrally formed with a shaft 15 which projectsthrough bight portion of support and face plate M. An operating knob maybe mounted on the shaft and secured thereto in a suitable manner such asby a set screw 31, the knob thus providing means for rotating cam 35 toadjust the force of spring 3|. Cam 35 also includes an additionalprojection 38 in addition to the main cam surface, and the purpose ofthis projection and the operation of the cam are explained in detailhereinafter.

The device H) has a main operating lever 4| which is pivoted on a pairof lanced and formed arms, or bosses, 42 which project out from verti-Member I2 includes an opening 43 to provide for the extension of lever4| therethrough, and arms 42 may conveniently be formed from metal whichpreviously lay along the sides of this opening. Lever 4| has on oppositesides thereof a pair of downwardly turned portions 44 which rest onbosses 4-2, and each portion 44 is provided with an additional smallprojection 45 extending downwardly along the inner edge of boss 42 toaid in maintaining the alignment of lever 4|.

The lever 4| has a transversely disposed indentation 45 in the uppersurface thereof in which is positioned an enlarged upper portion 41 ofoperating rod 25. Lever 4| also includes a slot at right angles with theindentation 45, which is similar to the slot previously described forretainer 26, to permit the passage of the lower enlarged portion ofoperating rod 25 through lever 4| during assembly. In the absence ofpressure in bellows 22, the spring 3| exerts a downward biasing forcewhich, acting through the enlarged upper portion 41 of the operating rodin indentation 46, tends to pull the right extremity (as seen in Figs. 1and 3) of lever 4| downward.

Near its right end, lever 4| has secured thereto in a suitable mannersuch as by a pair of rivets 86 an extension 48. This extension is ofinsulating material and extends beyond the end of lever 4| to one sideand below lever 4|, as shown best in Figs. 1, 3 and 8. A smallprojection 49 may be formed integrally with extension 48 on the lowersurface thereof, and in the open contacts position shown in Fig. 1 thisprojection is in engagement with a larger horizontal projection 5|] oninsulating support member l3. The engagement of projection 49 withprojection 50 limits the downward motion of the right end of lever 4|.

The insulating member l3 may be assembled conveniently with metal framemember II by means of four rectangular projections 5| on member II whichpass through four rectangular openings 52 in member I3 near the fourcorners thereof and are twisted as seen best in Figs. 1, 7 and 8, inorder to engage suitable cam surfaces 18 on member l3 and hold themember l3 securely to member II. The upper and lower legs of member I Ieach have a pair of projections 79 against which member l3 abuts, toprovide exact positioning of member l3.

The member I3 supports both the fixed and movable contact members of thedevice ID. As shown in Figs. 1, 6 and '7 particularly, the fixed contactmember 53 is positioned on a right angle terminal member 54. One portionof member 54 is secured to a sunken outer surface portion 8| of memberIS in a suitable manner such as by a pair of rivets 55, while the rightangle portion of member 54 extends into the device enclosure through asuitable opening 8|] in mem ber l3 and supports fixed contact member 53in horizontally disposed relation. Terminal member 54 may be providedwith a screw 56 by which an electrical conductor such as conductor 51may be secured thereto in order to provide an electrical connection tothe fixed contact of the switching mechanism.

A movable contact member 58 arranged for movement into and out ofengagement with fixed contact member 53 is secured to and is supportedby a resilient member 59 which is positioned in transversely disposedoperative relation with respect to extension 48 of lever 4| and isbiased toward contact 53. As illustrated in Figs. 6 and 7 particularly,resilient member 59 has a reversely bent portion 60 overlying extension48 to which the movable contact member 58 is secured. Resilient member59 is secured to and supported by a second terminal member 6| whichlikewise extends through opening 8!! in member l3 and has a right-angleportion secured to the sunken outer surface 8| thereof in a suitablemanner such as by a pair of rivets 62. A screw 63 is provided interminal 62 for an electrical connection to a conductor such as 54.

For biasing lever 4| upwardly, i. e., toward the contacts closedposition, there is provided a hairpin spring 65 which is best seen inFigs. 1, 3 and 9. Spring 65 has two indentations, one of which isengaged by a knife edge portion 6% on the right end of lever 4| whilethe other is engaged by a knife edge portion on a member 68. The lattermember may conveniently be secured to the top leg of frame I! by a pairof rivets 69. The member 68 is preferably of resilient material and, asshown in Fig. 9, there may be provided a set screw 10 threaded through asuitable opening in insulating member |3 which provides for theadjustment of knife edge 51 to the left or right to decrease or increasethe spacing between knife edges 66 and 61.

The parts of the switching mechanism, and particularly projections 49and 50, are so portioned and arranged that knife edge 66 on lever 4| isalways above a straight line connecting knife edge 61 and the pivotpoint of lever 4| where projections 44 rest on projections 42, i. e.,spring 65 biases the right end of lever 4| continuously upward. Thusspring 65 always exerts a contact closing force on lever 4| tending toforce the right end of lever 4| upward to cause projection 48 on thelever to engage the under side of projection 59 of resilient member 59and force movable contact member 58 up against fixed contact member 53.

The force exerted by spring 65 on lever 4| may be looked upon as havingtwo components, a horizontal component attempting to push knife edges 66and 6! apart and a vertical component tending to force the right end oflever 4| upward. The latter component increases very rapidly as theright end of lever 4| moves upwardly, and this action aids verymaterially in causing our mechanism to move from the contacts openposition to the contacts closed position with a snap action, asdescribed in greater detail hereinbelow. Similarly, the very rapiddecrease of this component of force aids in producing a snap action inthe opposite direction of movement, i. e., from contacts closed tocontacts open.

A cover plate 82, preferably of insulating material, may be provided forthe sunken outer portion of insulating member l3 and secured to memberl3 by means of a screw H which engages a suitable tapped opening 12 inthe outer surface of member l3. This cover plate protects the terminalsbut preferably does not cover set screw ll] as it is generally desirableto leave this available for adjustment.

At the opposite, or left end, lever 4| is provided with an enlargedportion 13 having a'pair of slightly upturned edges 13a. In the extremecounterclockwise position of control knob 36, shown in Fig. 4,projection 38 on the cam engages portion 13 of lever 4| and holds itfixed so that the lever cannot be pivoted regardless of the actions ofthe bellows and the spring members;

As will be readily understood, this is the off position of the switchingmechanism and when the knob is in this position the contacts 53, 58cannot be closed. There is provided a projection 14 extending outwardlyfrom the bight portion of support member into the path of projection 38which limits the rotation of knob 36 and cam 35 slightly less than acomplete revolution. In Fig. 4 the knob and cam are shown in the extremecounterclockwise position, while in Fig. 2, they are shown in theextreme clockwise position. In both extreme positions cam projection 38is in engagement with projection 14.

The device illustrated and described herein embodying the switchingmechanism of our invention may be advantageously used for automaticallyregulating the temperature of a house-v hold refrigerator, for example.In such a case, the tube 5! may contain a temperature responsive fluid.Upon an increase in the temperature. within the refrigerator to orbeyond a predetermined value, the pressure in tube 87 and hence inbellows 22 is increased enough to overcome the downward biasing force ofspring 3| sufficiently to allow the right end of lever 4| to be movedupwardly by spring 65. This results in the closing of contacts 53, 58with a snap action,'

the snap action being due in large measure to the rapid increase in theupward component of the force exerted by spring 65, as discussedpreviously. Two other features also contribute to the snap actionclosing of the contacts, namely, the action of resilient member 59which, as mentioned previously, is biased toward the fixed contact 53and immediately moves the movable contact member 55 in this direction assoon as it is released, and the hammer blow provided by projection 48 onthe under surface of projection 65 beneath movable contact member 58.When the temperature in the refrigerator is reduced sufficiently thatthe reduced pressure in bulb 22 is overcome by the spring 3|, theright-hand end of lever 4| again moves downwardly. This opens contacts53, 58, with a snap action due to the rapid decrease in the verticalforce com-'- open in the extreme counterclockwise position of cam andknob shown in Fig. i, by the action of cam projection 38 on lever 4|. Atall other positions of the cam and knob, the contacts will close whenthe pressure in bellows 22 reaches a predetermined amount correspondingto a temperature selected by the knob position. These selected pressuresand temperatures decrease as the knob and cam are rotated clockwise fromthe extreme counterclockwise position of Fig. 4.

position toward the contacts closed position, additional spring meansbiasing said lever continuously toward the contacts open position, saidadditional spring means normally overpowering said hairpin spring means,and condition responsive means for counteracting said additional springmeans to such an extent that said hairpin spring means causes saidcontacts to close with a snap action.

4. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means for movement between twopositons, a fixed contact member secured to said support means, aresilient member having as a portion thereof movable contact meansarranged to engage said fixed contact member secured to said supportmean in operative relation with said operating lever, said resilientmember being biased to move the movable contact portion thereof in apredetermined direction and having means providing for the movement ofthe resilient member responsively to the movement of said lever, saidcontacts being engaged in one position of said operating lever anddisengaged in the other position, spring means biasing said levercontinuously toward a first of its two positions, additional springmeans biasing said lever continuously toward the second of its twopositions, said additional spring means normally overpowering said firstspring means 9 and maintaining said lever in said second position, andcondition responsive means for partially counteracting said additionalspring means whereby said first spring means is enabled to move saidlever from said second position to said first position.

5. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means for movement between twopositions, a fixed contact member secured to said support means, aresilient member having movable contact means arranged to engage saidfixed contact member as a portion thereof and secured to said support inoperative relation with said operating lever, said resilient memberbeing biased toward the contacts closed position and having meansproviding for the movement thereof responsively to the movement of saidlever, said contacts being open in one position of said operating leverand closed in the other said position, spring means biasing said levercontinuously toward said other position, said spring means providing anincreasing component of force tending to close the contacts as the levermoves from said one position toward said other position, additionalspring means biasing said lever continuously toward said one position,said additional spring mean normally over powering said first springmeans and maintaining said contacts open, and condition responsive meansfor counteracting said additional spring means sufiiciently that saidfirst spring means causes said lever to move from said one position tosaid other position and close said contacts with a snap action.

6. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means for movement between twopositions, a fixed contact member secured to said support means, aresilient mem-' ber having movable contact means arranged to engage saidfixed contact member as a portion thereof and secured to said supportmeans in operative relation with said operating lever, said resilientmember being biased to move the movcomponent of force tending ablecontact portion thereof in a predetermined direction and having meansproviding for the movement of the resilient member responsively to themovement of said lever, said contacts being engaged in one said positionof the operating lever and disengaged in the other position,nonovercenter spring means biasing said lever continuously toward afirst of its two positions, said non-overcenter spring means providingan increasing component of force on the lever aiding its movement as thelever moves from its second position toward the said first position,additional spring means biasing said lever continuously toward the saidsecond of its two positions, said additional spring means normallyoverpowering said non-overcenter spring means and maintaining said leverin said second position, and condition responsive means forcounteracting said additional spring means to such an extent that saidnon-overcenter spring means causes said lever to move from said secondposition to said first position.

'7. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means, a fixed contact membersecured to said support means, a flexible member secured to said supportmeans in operative relation with said operating lever and having meansfor loosely receiving a portion of said lever, movable contact meansforming a portion of said flexible member and arranged for engagementwith said fixed contact member, said operating lever being movablebetween two positions in one of which it engages said flexible memberand holds said contacts engaged and in the other of which it engages theflexible member and holds the contacts out of engagement, said leverbeing disposed to provide a hammer blow on said flexible member uponmovement of the contacts to either the engaged or disengaged position,spring means biasing said lever continuously toward a first of its twopositions, additional spring means biasing said lever continuouslytoward the second of its two positions, said additional spring meansnormally overpowering said first spring means, and condition responsivemeans for counteracting said additional spring means to such an extentthat said first spring means causes said lever to move from said secondto said first position.

8. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means, a fixed contact membersecured to said support means, a flexible member secured to said supportin operative relation with said operating lever and having means forloosely receiving a portion of said lever, movable contact means forminga portion of said flexible member arranged for engagement with saidfixed contact member, said operating lever being movable between twopositions in one of which it engages said flexible member and holds saidcontact apart and in the other or" which it engages the flexible memberand holds the contacts in engagement and said lever being disposed toprovide a hammer blow on said flexible member upon movement to either ofthe two positions, spring means biasing said lever continuously towardthe contacts closed position, said sprlng means providing a rapidlyincreasing to close the contacts as the lever moves from the contactsopen position towards the contacts closed position, additional springmean biasing said lever continuously toward the contacts open position,said strain 11 additional spring means normally overpowering said firstspring means, and condition responsive means for counteracting saidadditional spring means to such an extent that said first spring meanscause said contacts to close.

9. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means, a fixed contact membersecured to said support means, an elongated resilient member secured tosaid support in operative relation with said operating lever and havingmeans for loosely receiving a portion of said lever, movable contactmeans mounted on said resilient member and arranged for engagement withsaid fixed contact member, said resilient member being biased to movesaid movable contact means in a predetermined direction with respect tosaid fixed contact member, said operating lever being movable betweentwo positions in one of which it engages said resilient member and holdssaid contacts engaged and in the other of which it engages the resilientmember and holds the contacts disengaged and said lever being disposedto provide a hammer blow on said resilient member upon movement toeither the contacts engaged or contacts disengaged position, springmeans biasing said lever continuously toward a first of its twopositions, additional spring means biasing said lever continuouslytoward the second of its two positions, said additional spring meansnormally overpowering said first spring means and holding said lever insaid second position, and condition responsive means for partiallycounteracting said. additional spring means whereby said first springmeans is enabled to move said lever from said second position to saidfirst position.

10. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means, a fixed contact membersecured to said support means, a flexible member secured to said supportmeans in operative relation with said operating lever and having meansfor loosely receiving a portion of said lever, movable contact meansforming a portion of said flexible member and arranged for engage mentwith said fixed contact member, said operating lever being movablebetween two positions, in one of which it engages said flexible memberand holds said contacts engaged and in the other of which it engages theflexible member and holds the contacts out of engagement, said leverbeing disposed to provide a hammer blow on said flexible member uponmovement of the contacts to either the engaged or disengaged position,noneovercenter spring means biasing said lever continuously toward afirst of its two positions, said non-overcenter spring means providing arapidly increasing component of force on the lever aiding its movementas it moves from its. second position toward the said first position,additional spring means biasing said lever continuously toward the saidsecond of itstwo, positions, said additional spring means normallyoverpowering the said non-overcenter spring means and holding said leverin said second position, and condition responsive means forcounteracting said additional spring means to such an extent thatnon-overcenter spring means moves said lever from said second to saidfirst position with a snap action.

11. An electric switch mechanism comp-rising,

support means, an operating lever pivotally mounted on said supportmeans, a fixed contact member secured to said support means, anelongated resilient member secured to said support in operative relationwith said operating lever and having means for loosely receiving aportion of said lever, movable contact means mounted on said resilientmember and arranged for engagement with said fixed contact member, saidresilient member being biased to move said movable contact means in apredetermined direction with respect to said fixed contact member, saidoperating lever being movable between two positions in one of which itengages said resilient member and holds said contacts engaged and in theother of which it engages the resilient member and holds the contactsdisengaged and said lever being disposed to provide a hammer blow onsaid resilient member upon movement thereof to either the contactsengaged or contacts disengaged position, non-overcenter hairpin springmeans biasing said lever continuously toward a first of its twopositions, additional adjustable spring means biasing said levercontinuously toward the second of its two positions, said additionalspring means normally overpowering said non-overcenter hairpin springmeans and holding said lever in said second position, and conditionresponsive means for partially counteracting said additional springmeans whereby said non-overcenter spring means is enabled to move saidlever from, said second to said first position.

12. An electric switch mechanism comprising, support means, an operatinglever pivotally mounted on said support means, a fixed contact membersecured to said support means, an elongated resilient member secured tosaid support in transversely disposed relation with said operating leverand having means for loosely receiving a portion of said lever, movablecontact means mounted on said resilient member and arranged forengagement with said fixed contact member, said resilient member beingbiased to move said movable contact means in a predetermined directionwith respect to said fixed contact member, said operating lever beingmovable between two positions in one of which it engages said resilientmember and holds said contacts engaged and in the other of which itengages the resilient member and holds the contacts disengaged and saidlever being disposed to provide a hammer blow on said resilient memberupon movement thereof to either the contacts engaged or contactsdisengaged position, non-overcenter hairpin spring means biasing saidlever toward a first of its two positions, additional adjustable springmeans biasing said lever toward the second of its two positions,saidadditional spring means including an operating rod operativelyengaging said lever and positioned substantially normally thereto and acoil spring surrounding said operating rod, said additional spring meansnormally overpowering said non-overcenter hairpin spring means andholding said lever in said second position, and condition responsivemeans operatively connected with said operating rod for partiallycounteracting said additional spring means to such an extent that saidnon-overcenter spring means causes said lever to move from said secondto said first position.

13. A condition responsive electric switch mechanism comprising, supportmeans, an operating lever pivotally mounted on said support means, afixed contact member secured to said support means, a cantilever springmember se cured to said support means in transversely disposed relationwith said operating lever and having a reversely turned portion on thefree end thereof for loosely receiving a portion of said operatinglever, a movable contact member mounted on said reversely turned portionand arranged for engagement with said fixed contact member, saidoperating lever being movable between two positions, in one of which itengages said cantilever spring member and holds said contacts inengagement and in the other of which it engages said resilient memberand holds the contacts apart, said lever being disposed to provide ahammer blow on said cantilever spring member upon movement to either thecontacts closed or the contacts open position, non-overcenter hairpinspring means biasing said lever toward the contacts closed position,additional adjustable spring means biasing said lever toward thecontacts open position, said additional spring means including anoperating rod extending through an opening in said lever on the sameside of the pivot point thereof as said contacts, said rod operativelyengaging said lever and being positioned substantially normally thereto,a retaining ring secured to said rod, a slidable spring adjustingbracket, and a coil spring surrounding said operating rod and positionedbetween said retaining ring and said bracket, said additional springmeans normally overpowering said non-overcenter hairpin spring means andmaintaining said contacts open, a

bellows engaging an end of said operating rod for partiallycounteracting said additional spring means to such an extent that saidnon-overcenter hairpin spring means is enabled to move said lever fromthe contacts open to the contacts closed position, an adjusting camengaging said bracket for adjusting the pressure at which said bellowscounteracts said additional spring means sufiiciently to enclose saidcontacts, a projection on said cam for engaging said lever on theopposite side of said pivot to hold said contacts open regardless of theaction of said bellows, and adjustment means for said hairpin spring toadjust the differential between the pressure at which said bellowscauses said contacts to close and the pressure at which said additionalspring means can overpower said hairpin spring means and said bellows toopen said contacts again.

ROBERT L. GRAY. CHARLES S. GRIMSHAW.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,011,918 Cheney Dec. 19, 1911 2,458,518 Kohl Jan. 11, 19492,537,431 Stickel Jan. 9, 1951

